Typically, a wafer comprising a plurality of semiconductor dice are mounted on an adhesive film during singulation wherein each individual die is separated while it adheres to the adhesive film. Detaching and picking up of a die from an adhesive film is thus a common process involved in die bonding and flip chip bonding processes for assembling an electronic package. One trend for the development of high density electronic devices is to multiply its density on the same footprint by stacking up the dice comprised in an electronic package. The thickness of each die being stacked in the package has to be reduced in order to minimize the final height of the package.
It becomes a challenging task to detach a die from an adhesive film without damaging the die when the thickness of the die is reduced to below 4 mils (about 100 microns). Dice with thicknesses of 3-4 mils (75-100 microns) have been used for mass production for some time. Mass production of dice at 2-3 mils (50-75 microns) thick is currently under preparation. Experiments for research and development in electronic packaging designs are ongoing for dice of 0.8-2 mils (20-50 microns) thick. Hence, an apparatus that is capable of reliably detaching very thin dice from adhesive films is becoming a critical machine in the realm of electronic assembly equipment.
Typically in a die bonding process, a die is detached and picked up from an adhesive or dicing film by ejecting and pick-up tools before the die is transferred to a substrate such as a lead frame, a printed wiring board (PWB) substrate or a surface of another die in stacking die applications. In a die pickup process, a designated die on a dicing film is aligned with an ejecting tool with push-up pins which raises the die from the underside while the dicing film is held down by vacuum suction. A collet or a pick-up tool is then positioned just above the top surface of the partially detached die while the die is being lifted from the dicing film when the push-up pins rise to an appropriate level. The collet provides vacuum suction to hold the die during the detachment process, as well as transfers the detached die from the dicing film to a bonding substrate.
There are various forms of die detachment and pick up tools for facilitating detachment of a die from a dicing film to which it is mounted. The conventional tools include a needle-type ejector pin design, which is a traditional design for detaching a small die from a dicing film. Other forms of detachment tools are pyramidal-type detachment tools and slide-type detachment tools.
FIG. 1 is an illustration of a conventional die detachment and pick-up tool 100 with needle-type ejector pins 102. The die detachment part of the tool 100 has an ejector comprising an ejector chuck 104, ejector pins 102 and an ejector cap 106. The pick-up part of the tool 100 has a collet 108 mounted on a collet body 109 and positioned above a die 110 located on a dicing film 112 which is in contact with an upper platform surface 107 of the ejector cap 106. Vertical movement of the ejector chuck 104 is driven by a motorised mechanism. The ejector pins 102 are positioned on top of the ejector chuck 104 and are movable with the ejector chuck 104. For small dice of dimensions such as 2×2 mm2, a single ejector pin 102 positioned at the center of the die 110 to be detached suffices to detach the die 110. Multiple ejector pins 102 are preferred for larger dice, and the ejector pins 102 are evenly distributed to achieve a uniform push-up force on the die 110 so as to reduce a pinching effect by the ejector pins 102.
The ejector chuck 104 and ejector pin/pins 102 are positioned within the ejector cap 106. A vacuum channel 114 is enclosed by the ejector cap 106 in order to provide vacuum suction for aiding in the delamination of the die 110 from the dicing film 112.
When the thickness of a die is reduced to less than 100 microns, the die becomes less rigid. To detach a die, peeling energy is applied to the die being detached via push-up motion of ejector pins and the vacuum suction on the dicing film in order to overcome a critical interfacial adhesion strength between the die and a dicing film. Deformation of the die may arise due to the pinching effect by the ejector pins and the bending of the die. When the applied peeling energy reaches the critical interfacial adhesion strength, the die may be detached from the dicing film. However, the die will crack or break when the process of deformation of the die also reaches the critical strength of the die. The critical strength of the die depends on various characteristics of the die, such as the material of the die, wafer thinning, pattern on the surface of die and sawing of the die. For conventional die pick-up using ejector pin or pins, the pinching effect and bending deformation are affected by the number, arrangement and geometry of the ejector pins. Furthermore, for a large die, the ejector pins located at the periphery of the die inhibit propagation of the detachment to the center of die. Therefore, a conventional pick-up tool using ejector pins may not be suitable for detaching a thin die from a dicing film.
The pyramidal-type detachment tool includes a plurality of annular connection members to detach a semiconductor chip from a dicing film by stages; from an outer circumferential portion of the semiconductor chip towards a central portion of the semiconductor chip. The annular connection members are sequentially raised commencing from an outer connection member to a central connection member to form a pyramidal shape. Like the conventional needle-type detachment tool, the raised annular connection members in a pyramidal shape apply stress to the semiconductor chip which may crack or damage as a result of the stress. For this reason, it may also be undesirable to apply the pyramidal-type pickup apparatus for the separation of a thin semiconductor chip from a dicing film.
The slide-type detachment tool includes a slide that moves from side to side and attracts a semiconductor chip by vacuum suction so that the semiconductor chip is separated from a dicing film. Since the slide forms a vacuum while the slide moves from side to side, the distance through which the slide is configured to move increases when the size of the semiconductor chip increases. Also, productivity is low when using the slide-type pickup detachment tool due to the low moving speed of the slide.
Examples of prior art for thin die detachment applications are highlighted as follows. US Publication Number 2007/0228539A1 entitled “Method For Detaching A Semiconductor Chip From A Foil And Device For Mounting Semiconductor Chips” discloses a method for detaching a chip from a dicing film such as a foil using a ramping surface with a stripping edge and ejector pins. The stripping edge is next to a groove area with the ejector pins. When detaching a die, the stripping edge moves up the surface of an ejector cap while vacuum suction is applied to the said ejector cap. The detached semiconductor is curved to form a concave shape when it is transported to the stripping edge by the movement of a wafer table. The detached chip is pushed to the groove and is picked up by ejector pins. A disadvantage of this detachment tool is having to move the wafer table to the stripping edge. In order to move the wafer table, vacuum suction force that is applied between the dicing film and the surface of the ejector cap must be low as the vacuum suction force would drag and distort the wafer. A lower vacuum suction however reduces the applied peeling energy. Furthermore as the detachment of the die is not on a controllable stage, the die may flip. Also, in the final pick-up stage, ejector pins are used which as discussed above are not suitable for picking up thin die.
US Publication Number 2002/0129899A1 entitled “Die Pickup Method And Die Pickup Apparatus” discloses a movable plate which may move horizontally or in both a horizontal plane and a vertical direction to detach a die from a dicing film. The shortcoming for this method is that there is no supporting structure underneath the die being picked when the movable plate is moved to detach the die. This may cause the die to crack at locations where the die is not detached. Additionally, neighbouring dice surrounding the die being picked are affected by the movable plate.
US Publication Number 2008/0092360A1 entitled “Thin Semiconductor Chip Pickup Apparatus and Method” discloses a die detachment apparatus with a stage for supporting a dicing film. An advantage over the movable plate discussed above is that the die detachment process is faster and the neighbouring dice are also not affected by the detachment process. However, this apparatus involves the motion of a suction member along a vertical axis at a level below the surface of the ejector cap which means the die is not pushed up very much away from the ejector cap. Furthermore, the initial detachment requires a dicing film to conform to the initial lowering of the suction member by applying suction vacuum. This greatly limits the applied peeling energy to the die being detached. Therefore, it would be desirable to achieve an effective method of detaching thin chips which provides support to the chip and reduces the pinching effect on the chip while avoiding the disadvantages of the prior art as discussed above.